1. Field of the Invention
The present invention relates to an external force measuring device suitable for use in detection of, e.g., an angular velocity, an acceleration, and so forth.
2. Description of the Related Art
In general, as external force measuring devices, angular velocity sensors have been known, each of which comprises a substrate, a mass supported displaceably in two orthogonal directions on the substrate via supporting beams, a vibration generating means for vibrating the mass in a vibration-direction parallel to the substrate in one of the two directions, and an angular velocity detection means for detecting the displacement of the mass caused when the mass is displaced in a detection-direction perpendicular to the vibration-direction (for example, Japanese Unexamined Patent Application Publication No. 5-312576).
In an angular velocity sensor produced in such a first conventional technique, the mass is vibrated at a predetermined amplitude, e.g., in the X-axial direction of the X and Y axial directions parallel to the substrate. In this state, if an angular velocity on the Z axis is applied, a Coriolis force acts on the mass, so that the mass is displaced in the Y-axial direction. Therefore, the angular velocity detection means detects the displacement of the mass as a variation in electrostatic capacitance or the like to output a detection signal corresponding to the angular velocity.
In this case, the mass is supported displaceably (vibration) in the X-axial direction and so forth by the supporting beams provided on the substrate. The supporting beams are fixed to the substrate on the base-ends thereof. The top ends thereof are connected to the mass. When the angular velocity sensor is operated, the supporting beams are deflected, and thereby, the mass is vibrated in the X-axial direction.
In a second conventional technique described, e.g., in Japanese Unexamined Patent Application PublicationNo. 7-218268, an angular velocity sensor, called a tuning fork, is used. A pair of masses, arranged on a substrate, are vibrated at opposite phases to each other. The vibration to be transmitted from the masses to the substrate via supporting beams is canceled out by means of a pair of the masses.
In this case, the supporting beams which support a pair of the masses have complicated shapes having plural flexed portions so that each of the masses can be supported at one site on the substrate. Moreover, the top ends of the supporting beams are branched and connected to the respective masses.
In the above-described first conventional technique, the mass is connected to the substrate via the supporting beams. Therefore, when the mass is vibrated on the substrate, the vibration is readily transmitted to the substrate side via the supporting beams.
For this reason, when the angular velocity sensor is operated, vibration energy is leaked toward the substrate side, so that the amplitudes and the vibration velocity of the mass are reduced, and a Coriolis force caused by the angular velocity is decreased. As a result, the detection sensitivity may be unstable. Moreover, when the vibration is transmitted to the substrate, the mass may be vibrated in the detection direction, due to vibration of the substrate, though no angular velocity is applied to the mass. Thus, this causes the problem that errors are readily generated in detection values of the angular velocity, and the reliability is deteriorated.
On the other hand, in the second conventional technique, the pair of masses are vibrated at opposite phases, so that the vibration to be transmitted to the substrate side is canceled out. However, these masses are supported by supporting beams having complicated flexed shapes. Therefore, in production of the sensor, it is difficult to render the supporting beams, e.g., the sizes, shapes, characteristics at deflecting, and so forth evenly with respect to the masses provided on the opposite sides.
For this reason, in the second conventional technique, dispersions in size and errors in working or the like of the supporting beams may cause a difference between the vibration states of the pair of the masses. Thus, there arises the problems that vibration of the respective masses transmitted to the substrate side cannot be stably canceled out.
On the other hand, when the angular velocity sensor is operated, and an acceleration in the Y-axial direction is added to the sensor, due to an external force of collision or the like, the masses may be displaced in the Y-axial direction, caused by not only the Coriolis force caused by the angular velocity but also the inertial force by the acceleration. Thus, the displacement comprising the angular velocity component and the acceleration component is detected as the angular velocity.
As a result, in the first conventional technique, even if collision or the like is slightly added to the angular velocity sensor, for example, the acceleration component, caused by the collision or the like, is contained as an error in an angular velocity detection signal, which deteriorates the detection accuracy of the angular velocity. Thus, there arises the problem that the reliability is enhanced with difficulty.
Especially, in the case in which the acceleration to be added to the sensor has a frequency component of which the frequency is near the vibration frequency of the masses, an error, caused by the acceleration component, can not be securely eliminated even if the detection signal is synchronously rectified and integrated at a constant period corresponding to the vibration frequency to carry out the signal processing such as synchronous detection or the like which extracts the angular velocity component.
In view of the above-described problems of the conventional techniques, the present invention has been devised. It is a first object of the present invention to provide an external measuring device in which vibration of masses can be prevented from being transmitted to the substrate side via supporting beams, the vibration state can be stably kept on the substrate, and moreover, the detection sensitivity and detection accuracy and reliability can be enhanced.
Moreover, it is a second object of the present invention to provide an external force measuring device in which even if both of the angular velocity and the acceleration are applied to the masses, at least the angular velocity can be accurately detected, separately from the acceleration, and the detection operation can be stabilized.
To solve the above-described problems, according to a first aspect of the present invention, there is provided an external force measuring device which comprises a substrate, plural masses opposed to and spaced from the substrate, arranged along the Y-axial direction of three orthogonal axial directions, that is, X-, Y-, and Z-axial directions, such as to be vibratable in the X-axial direction at opposite phases to each other by a vibration generator; supporting beams connecting the respective masses displaceably in the X-axial direction, fixing portions provided between the supporting beams and the substrate, and an external force detector for detecting, as the angular velocity or acceleration, a displacement of the respective masses in one of the Y-axial and Z-axial directions, caused when an angular velocity or an acceleration acts on the respective masses.
Owing to the above-described configuration, the plural masses can be connected by the supporting beams in the Y-axial direction perpendicular to the vibration direction (X-axial direction). For example, a part of the masses are vibrated by means of the vibration generator, and thereby, neighboring masses can be vibrated substantially at opposite phases. Thereby, on the sites in the middles of the supporting beams connecting the masses, the nodes of vibration can be arranged at which the supporting beams are positioned substantially constantly when the supporting beams, together with the respective masses, are vibrated.
Moreover, for example, two masses to be vibrated at opposite phases, when an angular velocity is applied, are displaced in the opposite directions, due to the Coriolis force, and when an acceleration is applied, are displaced in the same direction, due to the inertial force. Therefore, the angular velocity and the acceleration can be detected, distinguished from each other, by comparison of the displacements of the masses.
Preferably, the fixing portions connect to the substrate the sites of the supporting beams corresponding to the nodes when the respective masses are vibrated at opposite phases to each other.
Thereby, the fixing portions can fix the supporting beams to the substrate at the sites corresponding to the vibration nodes caused when the masses and the supporting beams are vibrated. Accordingly, the fixing portions can suppress vibration of the masses from being transmitted to the substrate side.
Additionally, the supporting beams may support the respective masses displaceably in the Z-axial direction, and the external force detecting means detects the displacement of the respective masses caused when the masses are displaced in the Z-axial direction.
Accordingly, the masses can be displaced in the Z axial direction correspondingly to an external force such as an angular velocity, an acceleration, and so forth, while the masses are being vibrated in the X-axial direction. Then, the displacement can be detected as an angular velocity or acceleration by the external force detector.
Also preferably, the respective masses comprise a first mass positioned in the center in the Y-axial direction, and second masses positioned on both of the sides in the Y-axial direction of the first mass, the first mass being supported by the supporting beams via mass-supporting beams displaceable in the Y-axial direction, and the external force detector detecting the displacement when the first mass is displaced in the Y-axial direction.
Accordingly, the second masses can be arranged in a symmetrical pattern, sandwiching the first mass. These masses can be stably vibrated at opposite phases in the X-axial direction. In this state, when the first mass is displaced in the Y-axial direction correspondingly to the angular velocity, the displacement can be detected as an angular velocity by means of the external force detector. Moreover, when no angular velocity is applied to the sensor, the first and second masses are vibrated only in the X-axial direction. At this time, the mass-supporting beams can be held so as not to be displaced in the Y-axial direction. Accordingly, the first mass can be prevented from being displaced in the Y-axial direction in error.
According to a second aspect of the present invention, there is provided an external force measuring device which comprises a substrate, a first mass opposed to and spaced from the substrate, arranged along the Y-axial direction of three orthogonal axial directions, that is, X-, Y-, and Z-axial directions, such as to be vibratable in the X-axial direction by a vibration generator; second masses provided on both of the sides in the Y-axial direction of the first mass so as to sandwich the first mass and to be vibrated in the X-axial direction by the vibration generator, third masses positioned between the first mass and the second masses so as to surround the first mass, supporting beams connecting the second masses to each other displaceably in the X-axial direction; connecting portions connecting the third masses to the supporting beams, mass-supporting beams the first mass to the third masses displaceably in the Y-axial direction; fixing portions provided between the substrate and the supporting beams and connecting the supporting beams to the substrate, and an external force detector for detecting, as an angular velocity, the displacement in the Y-axial direction of the first mass, caused when an angular velocity acts on the first mass, the first and third masses, and the second and fourth masses being vibrated at opposite phases to each other.
Accordingly, the first mass can be displaced in the Y-axial direction according to the angular velocity, while the first, second, and third masses are vibrated in the X-axial direction, by the vibration generator. When no angular velocity is applied to the sensor, the supporting beams are deflected in the X-axial direction, and thereby, the first, second, and third masses are vibrated only in the X-axial direction, and then, the first mass, surrounded by the third masses, can be held so as not to be displaced in the Y-axial direction. Therefore, the third masses can interrupt deflection or the like of the supporting beams from being converted to a displacement in the Y-axial direction and being transmitted to the first mass.
Preferably, the fixing portions connect to the substrate the sites of the supporting beams corresponding to the nodes caused when the first and third masses and the second mass are vibrated at opposite phases to each other.
Accordingly, the fixing portions fix to the substrate the sites of the supporting beams corresponding to the nodes caused when the first, second, and third masses and the supporting beams are vibrated. Thus, vibration of the respective masses can be prevented from being transmitted to the substrate side via the supporting beams.
Additionally, the masses may comprise a first mass positioned in the center in the Y-axial direction, and second masses positioned on both of the sides in the Y-axial direction of the first mass, and the first and second masses are connected to the supporting beams via the first and second mass supporting beams displaceable in the Y-axial direction, respectively.
Accordingly, the first and second masses can be vibrated in the X-axial direction via the supporting beams. In this state, the first mass can be displaced in the Y-axial direction, correspondingly to an external force, by the first-mass supporting beams. The external force detector can detect an angular velocity or acceleration.
According to a third aspect of the present invention, there is provided an external force measuring device which comprises a substrate, a first mass opposed to and spaced from the substrate, such as to be vibratable in the X-axial direction of three orthogonal axial directions, that is, X-, Y-, and Z-axial direction, by a first vibration generator, second masses provided on both of the sides in the Y-axial direction of the first mass so as to sandwich the first mass and to be vibrated in the X-axial direction by a second vibration generator, third masses positioned between the first mass and the second masses so as to surround the first mass, fourth masses surrounding the second masses, supporting beams connecting the fourth masses to each other displaceably in the X-axial direction, connecting portions connecting the third masses to the supporting beams, first mass supporting beams connecting the first mass to the third masses displaceably in the Y-axial direction, second mass supporting beams connecting the second masses to the fourth masses displaceably in the Y-axial direction, fixing portions provided between the substrate and the supporting beams and connecting the supporting beams to the substrate, and an external force detector for detecting, as an angular velocity or acceleration, the displacement in the Y-axial direction of the first and second masses, caused when an angular velocity or acceleration acts on the first and second masses, said first and third masses, and said second and fourth masses being vibrated at opposite phases to each other.
Accordingly, the first, second, third, and fourth masses can be vibrated in the X-axial direction. In this state, the first and second masses can be displaced in the Y-axial direction correspondingly to an external force by means of the first and second mass supporting beams. Moreover, the third mass can interrupt the deflection or the like of the supporting beams from being transmitted to the first mass. The fourth mass can interrupt deflection or the like of the supporting beams from being transmitted to the second mass.
Accordingly, the fixing portions can connect to the substrate the sites of the supporting beams corresponding to the nodes caused when the first, second, third, and fourth masses are vibrated. Thus, vibration of the respective masses can be suppressed from being transmitted to the substrate side via the supporting beams.
Moreover, the external force detecting means combines displacements of the respective masses caused when the masses are vibrated to opposite phases to be displaced in the Y-axial direction to detect, so that at least the angular velocity applied to the respective masses is separated from an acceleration and detected.
Accordingly, for example, two masses vibrating at opposite phases, when an angular velocity is added, are displaced in the opposite directions to each other, due to the Coriolis force, and the two masses, when an acceleration is added, are displaced in the same direction, due to the inertial force. Therefore, e.g., by subtracting the displacements of the respective masses, the components in the same direction (acceleration components) of these displacements can be canceled out to be removed. Thus, at least the angular velocity can be detected, separately from the acceleration.
Preferably, the external force detector comprises fixed detection electrodes positioned between the first mass and the second masses and provided on the substrate; first movable detection electrodes provided on the first mass and opposed to and spaced in the Y-axial direction from the fixed detection electrodes, and second movable detection electrodes provided on the second masses and opposed to and spaced in the Y-axial direction from the fixed detection electrodes, the external force detector detecting, in parallel, displacements of the first and second movable detection electrodes with respect to the fixed detection electrodes as variations in electrostatic capacitance.
Accordingly, if an angular velocity is applied to the respective masses while the first and second masses are vibrated at opposite phases, these masses are displaced in the opposite directions to each other, due to the Coriolis force. As a result, for example, both of the first and second movable detection electrodes can be positioned near the fixed detection electrodes, and the electrostatic capacitances between the fixed detection electrodes and the movable detection electrodes can be increased, correspondingly to the angular velocity. Moreover, if an acceleration is applied to the first and second masses, these masses are displaced in the same direction. Thus, one of the first and second movable detection electrodes can be positioned near the fixed detection electrode, and the other can be more separated from the fixed detection electrode. Thus, variations in electrostatic capacitances between the detection electrodes, caused by the acceleration, can be canceled out.
Preferably, the external force detector comprises a first displacement detecting portion for detecting a displacement caused when the first mass, which is one of the first and second masses vibrating at opposite phases to each other, is displaced in the Y-axial direction, a second displacement detecting portion for detecting displacements caused when the second masses are displaced in the Y-axial direction, and an external force operation section for individually operating the angular velocity and the acceleration, using the displacements detected by the first and second displacement detecting portions.
Accordingly, the first and second displacement detecting portions can detect the displacements caused when the first and second masses vibrating at opposite phases are displaced in the Y-axial direction. If both of an angular velocity and an acceleration are applied, the two detection values include angular velocity components of the first and second masses displaced in the opposite directions correspondingly to the angular velocity, and acceleration components of the first and second masses displaced in the same direction correspondingly to the acceleration. Therefore, in the external force operation section, the angular velocity and the acceleration can be individually operated by addition or subtraction of these two detection values.
Preferably, the external force detector comprises fixed detection electrodes each having plural electrodes fixedly formed in an interdigitated pattern on the substrate, and movable detection electrodes formed on the masses and having plural electrode plates formed so as to be interdigitatedly engaged with and spaced from the plural electrodes of the respective fixed detection electrodes in the Y-axial direction, and the external force detection means detecting variations in electrostatic capacitance between the fixed detection electrodes and the movable detection electrodes as the displacements of the masses.
Accordingly, the electrode plates of the fixed detection electrodes and the movable detection electrodes are interdigitatedly engaged with each other, so that large areas between the opposed detection electrodes can be produced. When the masses are displaced in the Y-axial direction, caused by an external force, the displacements can be detected as variations in distance (electrostatic capacitance) between the detection electrodes.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.